This document provides an overview of additional aspects of acid-base equilibria, including:
1. Important relations for pH, pOH, Ka, and Kb calculations.
2. Steps for calculating pH, pKa, [H+], Ka for acids or bases, including distinguishing between strong and weak acids/bases.
3. Steps for calculating pH for mixtures of acids and bases, including considerations for salt solutions, buffer solutions, and calculating pH changes upon adding small amounts of acid or base to a buffer.
pH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions (H+). Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations. The pH scale is not an absolute scale; it is relative to a set of standard solutions whose pH is established by international agreement.
pH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions (H+). Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations. The pH scale is not an absolute scale; it is relative to a set of standard solutions whose pH is established by international agreement.
Biochemical Oxygen Demand and its Industrial SignificanceAdnan Murad Bhayo
BOD is the amount of dissolved oxygen needed by aerobic biological organism in a body of water to breakdown organic material present in a given water sample at certain temperature over a specific time period .
Most of Bacteria in the aquatic columns are aerobic. Escherichia coli, Bacillus subtilis, Vibrio cholera.
Atmosphere contains 21% oxygen (210000 mg/dm3)
Higher the temperature of water higher will be the rate of respiration. So, concentration of oxygen decreases.
Many Animal species can grow and reproduce normally when dissolved oxygen level is ~ 5.0 mg/L.
HYPOXIA: When dissolve oxygen content below 3.0 mg/L. Many Species move elsewhere and immobile species may die
ANOXIA: When dissolve oxygen content below 0.5 mg/L. All aerobic species will die
Fertilizer contains Nitrate contributes to high BOD
Phosphate present in Soap and detergent that enhances the growth of algal blooms. As a result depletion of oxygen occur.
In a body of water with large amount of decaying organic material , the dissolved oxygen level may drop by 90 %, this would represent High BOD
In a body of water with small amount of decaying organic material , the dissolved oxygen level may drop by 10 %, this would represent Low BOD
ANALYSIS OF BOD OF WATER
Use glass bottles having 60 mL or greater capacity. Take samples of water.
Turn on the constant temperature chamber to allow the
controlled temperature to stabilize at 20°C ±1°C.
Record the DO level (ppm) of one immediately.
Place water sample in an incubator in complete darkness at 20 C for 5 days. Exclude all light to prevent possibility of photosynthetic production of DO
If don't have an incubator, wrap the water sample bottle in aluminum foil or black electrical tape and store in a dark place at room temperature (20o C or 68 °F).
DILUTION OF SAMPLE
Most relatively unpolluted streams have a BOD5 that ranges from 1 to 8 mg/L
Dilution is necessary when the amount of DO consumed by microorganisms is greater than the amount of DO available in the air-saturated.
If the BOD5 value of a sample is less than 7 mg/L, sample dilution is not needed.
The DO concentration after 5 days must be at least 1 mg/L and at least 2 mg/L lower in concentration than the initial DO
(American Public Health Association and others, 1995).
BOD of the dilution water is less than 0.2 mg/L.
Discard dilution water if there is any sign of biological growth.
pH of the dilution water needs to be maintained in a range suitable for bacterial growth
Bacterial growth is very good between 6.5 to 7.5
Sulfuric acid or sodium hydroxide may need to be added to the dilution water to lower or raise the pH, respectively.
CALCULATION:
The general equation for the determination of a BOD5 value is:
BOD = D1-D2/P
Where
D1 = initial DO of the sample,
D2 = final DO of the sample after 5 days, and
P = decimal volumetric fraction of sample used.
If 100 mL of sample a
Lecture materials for the Introductory Chemistry course for Forensic Scientists, University of Lincoln, UK. See http://forensicchemistry.lincoln.ac.uk/ for more details.
Biochemical Oxygen Demand and its Industrial SignificanceAdnan Murad Bhayo
BOD is the amount of dissolved oxygen needed by aerobic biological organism in a body of water to breakdown organic material present in a given water sample at certain temperature over a specific time period .
Most of Bacteria in the aquatic columns are aerobic. Escherichia coli, Bacillus subtilis, Vibrio cholera.
Atmosphere contains 21% oxygen (210000 mg/dm3)
Higher the temperature of water higher will be the rate of respiration. So, concentration of oxygen decreases.
Many Animal species can grow and reproduce normally when dissolved oxygen level is ~ 5.0 mg/L.
HYPOXIA: When dissolve oxygen content below 3.0 mg/L. Many Species move elsewhere and immobile species may die
ANOXIA: When dissolve oxygen content below 0.5 mg/L. All aerobic species will die
Fertilizer contains Nitrate contributes to high BOD
Phosphate present in Soap and detergent that enhances the growth of algal blooms. As a result depletion of oxygen occur.
In a body of water with large amount of decaying organic material , the dissolved oxygen level may drop by 90 %, this would represent High BOD
In a body of water with small amount of decaying organic material , the dissolved oxygen level may drop by 10 %, this would represent Low BOD
ANALYSIS OF BOD OF WATER
Use glass bottles having 60 mL or greater capacity. Take samples of water.
Turn on the constant temperature chamber to allow the
controlled temperature to stabilize at 20°C ±1°C.
Record the DO level (ppm) of one immediately.
Place water sample in an incubator in complete darkness at 20 C for 5 days. Exclude all light to prevent possibility of photosynthetic production of DO
If don't have an incubator, wrap the water sample bottle in aluminum foil or black electrical tape and store in a dark place at room temperature (20o C or 68 °F).
DILUTION OF SAMPLE
Most relatively unpolluted streams have a BOD5 that ranges from 1 to 8 mg/L
Dilution is necessary when the amount of DO consumed by microorganisms is greater than the amount of DO available in the air-saturated.
If the BOD5 value of a sample is less than 7 mg/L, sample dilution is not needed.
The DO concentration after 5 days must be at least 1 mg/L and at least 2 mg/L lower in concentration than the initial DO
(American Public Health Association and others, 1995).
BOD of the dilution water is less than 0.2 mg/L.
Discard dilution water if there is any sign of biological growth.
pH of the dilution water needs to be maintained in a range suitable for bacterial growth
Bacterial growth is very good between 6.5 to 7.5
Sulfuric acid or sodium hydroxide may need to be added to the dilution water to lower or raise the pH, respectively.
CALCULATION:
The general equation for the determination of a BOD5 value is:
BOD = D1-D2/P
Where
D1 = initial DO of the sample,
D2 = final DO of the sample after 5 days, and
P = decimal volumetric fraction of sample used.
If 100 mL of sample a
Lecture materials for the Introductory Chemistry course for Forensic Scientists, University of Lincoln, UK. See http://forensicchemistry.lincoln.ac.uk/ for more details.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Exploiting Artificial Intelligence for Empowering Researchers and Faculty, In...Dr. Vinod Kumar Kanvaria
Exploiting Artificial Intelligence for Empowering Researchers and Faculty,
International FDP on Fundamentals of Research in Social Sciences
at Integral University, Lucknow, 06.06.2024
By Dr. Vinod Kumar Kanvaria
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Normal Labour/ Stages of Labour/ Mechanism of LabourWasim Ak
Normal labor is also termed spontaneous labor, defined as the natural physiological process through which the fetus, placenta, and membranes are expelled from the uterus through the birth canal at term (37 to 42 weeks
Embracing GenAI - A Strategic ImperativePeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
Azure Interview Questions and Answers PDF By ScholarHat
CM4106 Review of Lesson 3 (Part 1)
1. CM4106 Chemical Equilibria & Thermodynamics
Lesson 3 (Part 1)
Additional Aspects of Acid-Base Equilibria
(Topic 3.1 – 3.5)
A Chemistry Education Blog by Mr Tan
http://chemistry-mr-tan-yong-yao.blogspot.sg/
3. (I) Calculations for acids OR bases
pH, pKa, [H+], Ka pOH, pKb, [OH–], Kb
Step 1: Determine what is present in the solution.
(A) Acid : Strong Acid vs Weak Acid
Monoprotic Acid / Diprotic Acid / Triprotic Acid
Concentration of Acid
(B) Base: Strong Base vs Weak Base
Monoprotic base / Diprotic base / Triprotic base
Concentration of Bas
Take note of concentration of acid / bases
(For dilute solutions, we need to take into consideration of
[H+] / [OH-] from auto-ionization from water)
Step 2: Use the appropriate equations for the respective species.
4. (I) pH calculations of Acid OR Base
x2
Ka =
Strong Acid Weak Acid ([HA] – x)
Strong acids dissociate HA(aq) ⇌ H+(aq) + A-(aq)
completely into ions in
aqueous solution.
I [HA] 0 0
C -x +x +x
[H+] = [HA] E [HA] - x +x +x
x2
Kb =
Strong Base Weak Base ([B] – x)
Strong bases dissociate B + H2O ⇌ BH+ + OH-
completely into ions in
I [B] - 0 0
aqueous solution.
C -x - +x +x
[OH-] = [B] E [B] - x - x x
5. (I) pH calculations of Acid OR Base
1. Determine if acid/ base is strong or weak (more common)
2. For weak acids, if asked to determine Ka, pH or [H+], you can save time by
using the formula:
[H+] = Ka × c [OH–] = Kb × c
Assumption: x is negligible
Example:
Calculate the pH of 0.50M HF solution at 25ºC where the Ka = 7.1 x 10-4
[H+][F-] x2
Ka = = = 7.1 x 10-4
[HF] (0.50 – x)
Assumption: For weak acids, x must be very small 0.50 – x ≈ 0.5
x2
= 7.1 x 10-4 x = [H+] = 0.0188 M Assumption is valid;
0.50
x < 5% of [HF]initial
pH = 1.73 (to 2 d.p.)
6. Calculate the pH of the following solutions at 298K
0.10 mol dm−3 CH3COOH (pKa = 4.75) Weak acid solution
(monoprotic acid)
CH3COOH(aq) + H2O (l) ⇌ CH3COO(aq) + H3O+(aq)
Initial (M) 0.10 - 0.00 0.00
Change (M) -x - +x +x
Eqm (M) 0.10 - x - +x +x
[CH3COO][H3O+] x2
Ka = = = 10 4.75 = 1.79 x 10-5
[CH3COOH] (0.10 – x)
Assumption: For weak acids, x must be very small 0.10 – x ≈ 0.10
x2 Remember to validate Assumption
= 1.79 x 10-5 Assumption is justified,
0.10
x < 5% of [CH3COOH]initial
x = [H3O+] = 1.338 x 10-3 M
Concentration: 2 s.f.
pH = 2.87 ( 2 d.p.) pH: 2 d.p.
7. (II) Calculations for mixture of acids AND bases
pH, pKa, [H+], α pOH, pKb, [OH–]
Step 1: Determine what is present in the solution.
(A) acid Stoichiometric amounts of acid and base –
base salt solution
(B) buffer Non-stoichiometric amounts of acid and
base – likely to be a buffer
(C) salt
Step 2: Use the appropriate equations for the respective
species.
8. (II) (a) or (c) pH calculation of salt solutions
COVERED IN GREATER DETAILS IN TOPIC 3.8
Salt solutions can be (i) neutral (ii) weak acids or (iii) weak bases
Basic Salt
CH3COONa (aq) → CH3COO- (aq) + Na+ (aq)
CH3COO- (aq) + H2O (l) ⇌ CH3COOH (aq) + OH- (aq)
conjugate base pH > 7
Acidic Salt
NH4Cl (aq) → NH4+ (aq) + Cl- (aq)
NH4+ (aq) + H2O (l) ⇌ NH3 (aq) + H3O+ (aq)
conjugate acid pH < 7
9. (II) (b) pH of Buffer Solutions
Acid Buffer weak acid + conjugate base
weak acid Assume negligible dissociation of acid due to common ion effect
CH3COOH(aq) + H2O(l) ⇌ CH3COO-(aq) + H3O+(aq)
CH3COONa(aq) → CH3COO-(aq) + Na+(aq)
conjugate base
Assume full dissociation of salt [salt]
pH = pKa + lg
(strong electrolyte) [acid]
Basic Buffer weak base + conjugate acid
weak base Assume negligible dissociation of base due to common ion effect
NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq)
NH4Cl(aq) → NH4+(aq) + Cl-(aq)
conjugate acid
Assume full dissociation of salt
(strong electrolyte) pOH = pKb + lg [salt]
[base]
10. (II) (b) pH of Buffer Solutions
1. Determine if buffer is acidic/ basic
2. When using H-H equation, you can save time by just
calculating no. of moles of salt and acid/base since total
volume is the same and cancels out. Useful for MCQs!
nsalt/V nsalt/V
pH = pKa + lg pOH = pKb + lg
nacid/V nbase/V
3. Need to be sensitive to the condition (maximum
buffering capacity)
where [salt] = [acid] which simply means pH = pKa
Similarly for basic buffer,
[salt] = [base] pOH = pKb
11. [salt]
pH pK a lg
Sample Calculation [acid]
• Find the pH of a buffer made from adding 3.28 g of sodium
ethanoate, CH3COO-Na+ to 1.00 dm3 of 0.0100 M ethanoic acid,
CH3COOH . (Ka = 1.80 x 10-5)
Useful Information
Molar Mass of CH3COO-Na+ = 82.03 g/mol
Amount of CH3COO-Na+ present in 3.28 g = (3.28 g / 82.03)
= 0.0400 mol
[CH3COO-Na+] = 0.0400 M
[CH3COOH] = 0.0100 M
[salt]
pH pK a lg
[acid]
5 0.0400
lg(1.80 10 ) lg pH = 5.3466
0.0100 = 5.347 (3 d.p.)
Page 46
12. An alternative approach –
Sample Calculation ICE Table
• Find the pH of a buffer made from adding 3.28 g of sodium ethanoate,
CH3COO-Na+ to 1.00 dm3 of 0.0100 M ethanoic acid, CH3COOH.
(Ka = 1.80 x 10-5)
n(CH3COO-Na+) present in 3.28 g = (3.28 g / 82.03)
Useful Information = 0.0400 mol
Molar Mass of CH3COO -Na+ = 82.03 g/mol
[CH3COO-Na+] = 0.0400 M
[CH3COOH] = 0.0100 M
CH3COOH(aq) + H2O (l) ⇌ H3O+ (aq) + CH3COO (aq)
Initial [ ] (M) 0.0100 M - 0 0.0400 M
Change [ ] (M) -x - +x +x
Equilibrium [ ] (M) 0.0100 - x - x 0.0400 + x
Ka =
[H3O+][CH3COO-] x (0.0400 + x)
= = 1.80 x 10-5
[CH3COOH] (0.0100 – x)
Solve for x, pH = - lg [H3O+] = - lg (4.497 x 10-6)
x = [H3O+] = 4.497 x 10-6 M
= 5.3470
= 5.347 (3 d.p.)
13. Calculating pH change after small amounts of
acid / base is added to buffer solutions
1) Determine new [salt]new and [acid]new / [base]new
How?
a) Determine n(acid / base) added to buffer solution
b) Determine the change to n(salt)buffer and n(acid)buffer /
n(base)buffer by considering the neutralization action of a
buffer
c) Determine new total volume of the buffer solution
[salt]new
pH new pK a lg
[acid] new
14. CM4106
Chemical Equilibria &Thermodynamics
Review of Pre-Quiz 3
Topic 3 (3.1 – 3.5)
Additional Aspects of Acid-Base Equilibria
Buffer Solutions, pH calculation, Maximum Buffer Capacity
15. Question 1 (a)
• Hypochlorous acid, HOCl, is a weak acid commonly
used as a bleaching agent. It dissociates in water as
represented by the equation below.
HOCl(aq) + H2O(l) ⇌ OCl-(aq) + H3O+(aq)
Ka = 3.2 x10-8
a) Write the equilibrium-constant expression for the
dissociation of HOCl in water.
[OC l ][H 3O ]
Ka
[HOC l ]
16. Question 1(b)
b) Calculate the molar concentration of H3O+ in a
0.14 M solution of HOCl.
HOCl(aq) + H2O(l) ⇌ OCl-(aq) + H3O+(aq)
Ka = 3.2 x10-8
HOCl (aq) + H2O (l) ⇌ H3O+ (aq) + OCl- (aq)
Initial [ ] (M) 0.14 - 0 0
Change [ ] (M) -y - +y +y
Equilibrium [ ] (M) 0.14 – x - x y
y2 Solve for y,
Ka
(0.14 y)
y = 6.7 x 10-5
y2
3.2 10 8 [H3O+] = 6.7 x 10-5 M (2 s.f.)
(0.14 y )
Note: units must be present
17. Question 1 (c)
c) A mixture of HOCl and sodium hypochlorite
(NaOCl) can be used as a buffer.
Write two equations to show how this buffer solution
can control pH.
• Addition of H3O+:
OCl(aq) + H3O+(aq) HOCl(aq) + H2O(l)
Note: state symbols must be present
• Addition ofOH :
HOCl(aq) + OH(aq) OCl (aq) + H2O(l)
18. Question 1(d)
HOCl reacts with NaOH according to the reaction represented
below:
HOCl(aq) + OH-(aq) OCl-(aq) + H2O(l)
Bob, a budding young chemist, decides to make a buffer by
adding a volume of 10.0 mL of 0.56 M NaOH to 50.0 mL of 0.14 M
HOCl solution. Assume that the volumes are additive.
HOCl(aq) + H2O(l) ⇌ OCl-(aq) + H3O+(aq)
Ka = 3.2 x10-8
Preliminary Considerations:
Reaction of NaOH with HOCl will form NaOCl (salt containing conjugate
base OCl-).
Hence, if HOCl is in excess, the final mixture will contain some excess
HOCl that is unreacted and some NaOCl formed as a result of the
neutralization reaction. BUFFER SOLUTION (Mixture of acid and
conjugagte base (salt)
19. Question 1(d)(i)
• Calculate the pH of the buffer solution
Henderson-Hasselbalch Equation to
[salt]
pH pK a log calculate pH of buffer equation
[acid] Need to determine [salt] / [acid]
HOCl (aq) + NaOH (aq) NaOCl (aq) + H2O(l)
n HOCl = (50.0/1000)(0.14) = 7.0 x 10-3 mol (excess reagent)
n NaOH = (10.0/1000)(0.56) = 5.6 x 10-3 mol
Total Volume = 50.0 + 10.0 = 60.0 cm3 = 0.0600 L
n HOCl remaining n NaOCl formed = 5.6 x10-3 mol
= 7.0 x 10-3 - 5.6 x 10-3
= 1.4 x 10-3 mol
[OCl] = 5.6 x 10-3 mol / 0.0600 L
[HOCl] = 1.4 x 10-3 mol / 0.0600 L = 9.33 x 10-2 M
= 2.33 x 10-2 M
20. Question 1(d)(i)
• Calculate the pH of the buffer solution.
[HOCl] = 1.4 x 10-3 mol / 0.0600 L [OCl] = 5.6 x 10-3 mol / 0.0600 L
= 2.33 x 10-2 M = 9.33 x 10-2 M
[salt]
pH pK a log
[acid]
8 (9.33 10 -2 )
pH lg(3.2 10 ) lg
(2.33 10 -2 )
pH 8.097
21. Question 1(d)(ii)
• Bob would like to prepare a new buffer solution. How many
grams of solid NaOH must he add to a 50.0 mL of 0.20 M HOCl
to obtain a buffer that has a pH of 6.0?
• Assume that the addition of the solid NaOH results in a
negligible change in volume. (Mr NaOH = 40)
Let the no of mole of NaOH required be y mol:
n HOCl = (50/1000)(0.20) = 0.01 mol n HOCl remaining = (0.01 - y) mol
n NaOH = y mol n NaOCl formed = y mol
NaOH (s) + HOCl (aq) NaOCl (aq) + H2O (l)
22. Question 1(d)(ii)
• Bob would like to prepare a new buffer solution. How many
grams of solid NaOH must he add to a 50.0 mL of 0.20 M HOCl
to obtain a buffer that has a pH of 6.0?
• Assume that the addition of the solid NaOH results in a
negligible change in volume. (Mr NaOH = 40)
n HOCl remaining = (0.01 - y) mol Total Volume = 50.0 mL = 0.0500 L
n NaOCl formed = y mol
y
[salt]
6.0 - log (3.2 x 10 ) lg 0.0500 y
pH pK a log
-8
1.4949 lg
[acid] 0.01 y 0.01 y
0.0500
Solve for y,
Mass of NaOH (s) required y
= 3.101 x 10-4 x 40 y = n (NaOCl) formed 10 1.4949
= n (NaOH) required
0.01 y
= 0.1240 g
= 3.101x 10-4 mol